Again, it may seem unlikely that there can be pairing for life inspecies, like the chaffinch of northern Europe and, with us, ofScotland, in which the sexes separate and migrate separately. Also ofnon-gregarious species like the nightingale in which the males arrive inthis country several days before the females. Yet I am confident that ifwe could catch and mark a considerable number of pairs it would be foundthat the same male and female found one another and re-mated every month.

It comes to this, that birds may pair for life, yet not be all the timeor all the month together, as in the case of hawks, crows, owls, herons,and many others. In numberless species which undoubtedly pair for lifethe sexes keep apart during several hours each day, and there is someevidence that those that separate for a part of the month remain faithful.